Work in our laboratory has continued on the investigations of immunologic reactions produced against prostatic tumor antigens utilizing the Dunning R3327 adenocarcinoma of the Copenhagen rat as a model system. Our ultimate goal is to determine whether humoral and cell mediated immunologic responses can be produced against tumor antigens of this prostatic cancer by conventional immunization techniques and by treatment of primary tumors by cryosurgery. If such responses can be detected, we wish to correlate the findings with the fate of metastatic lesions in the tumor-bearing animals. Specifically, is there a cause and effect relationship between anti-tumor immunity and regression of metastases? Toward that end our experiments have shown that (1) R3327 tumors can be destroyed by cryosurgical treatment; (2) Both in vitro and in vivo cell-mediated immune responses to the tumor can be induced by conventional immunization techniques; (3) a degree of protective immunity to the tumor can be induced both by conventional techniques and by cryosurgery and (4) different forms of the tumor have arisen both in vivo and in vitro (using a tissue culture line), each having different characteristics and possibly reacting differently to cryosurgical and immunological stimuli.